Gold II Nasus main here I can give you some tips. Nasus is a duelist and is a counter to most attack speed champions, however, some matchups are skill based.
Edit: I just looked at some of your past games with Nasus. Your builds are largely TERRIBLE. Build 
or 
and FULL TANK after that. Don't build crit chance, don't build 
or 
. Nasus does not need any lifesteal because of his passsive, he does not need any damage because of his Q he ONLY needs tank stats and ONE damage item. If you are wondering on a very basic build go 
and one of the above mentioned damage items. Build 
if you can't afford to die and are the carry. Of course you should adjust your builds to the game but Nasus builds very statically due to his kit. He does not need much else besides resistances and one damage item.
When you have a 
on the opposing team you need to itemize appropriately against them AND you have to pay attention to what they have, their positioning, and if the adc is with company.
- Build against these champions no matter what you need the stacking attack speed slow from the cold steel passive and the FH passive.
- Situationally build if you have trouble catching you will need the AoE slow sometimes if they are good
- Situationally build
. Thornmail is a bad item BUT if the opposing team is almost ALL AD (so only the support is AP) you can buy it as your 5th or 6th item. Don't buy it any earlier because it sucks without additional armor. Note, that if you build you other 2 items need A LOT of health. Warmogs, which is considered a bad item on Nasus, is justifiable in those instances.
- Build
if the enemy team has lower CC. If 3 of the opponents have different types of CC don't build it and build . You need to gap close to deal damage. I think ninja tabi is a better item against these champions HOWEVER if you can't get to them it doesn't matter.
- Take ghost
instead of 
. This is your gap closer and you will use this to kill one of them. Pop ghost at the start of the fight if they try to kite you.
- MAX Wither second if these champions are in the game instead of your Spirit fire. I typically max wither second in general, some nasus players max spirit fire only, and others max either or by the situation. So why should you max wither over spirit fire? These champions don't build much armor, it is more important to gap close against these champions, the potency of the movement speed slow AND the attack speed slow increases with each point.
- This means you have a maxed out wither, a and you should be able to effectively duel these champions if they do not have help and you pay attention to your positioning. You are really slowing their attack speed through items and the potency of your wither and you will be able to catch them with ghost
- Check to see if any of them have
this is important because if they have it, it means it will take a second wither to land before you can all in them. If this is mid game and you are still going down your itemization route and they have this item you may not be able to fight them.
- Nasus should be able to out duel any of these champions if the champion does not have the support with them AND they are both of comparable skill
On dueling she is the hardest to duel of the 3 and probably the most dangerous
- If she condemns you into a wall you probably have lost the fight due to the duration of the stun if the vayne is good she will begin fighting you buy popping her ult, tumbling to position for a condemn and killing you into the wall for the stun.
- Approach Vayne from the lane not from the jungle which gives her more likely chance for her to hit you into a wall
- If her is up you probably cannot fight her if this is late game. If it is not up you can fight and win because it will only take 2-3 Qs to kill. NOTE if she has Heal it will take 1 more Q depending on how well you are stacked. Pay attention if she has used her summoner. That can be the difference int he fight
On dueling
- Kogmaw needs help when fighting and he is easily killed if he has not one protecting him. While Vayne and Jinx have more agency in their kits if you gap close on Kogmaw he is for the most part dead.
- Kogmaw does mixed damage so you will need some magic resist against him you should have a 50/50 split in your build verse him
- You can pretty much approach him from the best route - if kogmaw tried to kite you pop ghost if he has no help.
- Good kogmaws when they realize they are dead will stand and auto you, this is how they max out their damage output when they know they can't escape. Be really careful because he will melt you in the late game just by doing this.
- In general, I don't group with my team too often against Kogmaws and almost split-push the whole game. Kog has good wave clear so you need to have too angles of approach to the enemy base. If you team fight he will largely melt you before you can do anything so if the kogmaw is strong just avoid grouping in general
On dueling - Jinx is the easier of the three due to her kit
- Jinx usually needs a baby sitter and her damage is not mixed so she isn't going to kill you that fast compared to the other two ADCs with Vayne's true Damage and Kogmaws magic damage.
- Jinx has no escapes so after she uses her traps and her slow she is pretty much dead. Side step the traps if she uses them early (if you get trapped you can still kill her if she isn't that strong) and dodge the slow.
- Jinx is one of my favorite ADCs because no matter how fed she gets Nasus CAN duel her. It is just a matter of whether she gets protection or not. No protection equals a dead jinx if she is near a Nasus.
- I always reassure my teammates if a Jinx gets fed to not worry about her because as long as the other opponents are not too strong she can easily be taken out even with a QSS.
I hope this helps. I do think that these are skill based matchups with ADCs having a slight edge on Nasus in a duel if they have damage. You need to dodge abilities, pay attention to what summoners they have, pay attention if they have QSS and if it is up, max wither over spirit fire, and pay attention to your approach. You cannot simply think because you have armor, health, and stacks that you can duel them in the late game. Vayne is the trickiest of the three, but while Vayne is a tank kill Nasus counters attack speed champions like her.
is a counterpick 2 
super strong attack speed slow 
because it allows you to gap close on them. This is a core item I see all Nasus mains in high elo build.
apprehend matches vayne's auto attack range and cannot be QSSd to the best of my knowledge.
Spirit pull can create a psuedotarget for illaoi and her team that can be used to chunk vayne incredibly hard.
Once this guy gets rylais, an ultimate on vayne will screw her over since she can qss one tick of slow but then it gets reapplied and stays on her for so damn long.
Pillar
